In the land environment, there are many known types of enclosures for bounding off certain areas in order to prevent the entry or exit of persons or animals. In zoological gardens or outdoor theme parks, the most customary enclosures are made of concrete walls, ditches, metallic netting or lattices which protect people against possible aggressions by the wild animals, bounding off the zones in which persons and animals may walk.
Simple solutions are also known of normal or barbed wire fences connected to a source of electricity to produce slight discharges when an animal comes into contact with them, even though these solutions are more suited to herds of cattle, sheep or horses.
In order to protect certain activities which are carried out under water, solutions are known which are based on fixed structures which totally enclose a space surrounded by open water. These are facilities of raft or swimming pool type, which contain sea water and form totally enclosed spaces denying access to predatory animals which could seriously endanger the activities of breeding, scientific research, or any other similar ones. There are also known registers connected to nets of every type, even though they are solutions which are heavily criticized by the animal protection societies because many animals die imprisoned in them.